The growing need for high data rate multi-media communications requires wideband wireless communication systems. This requirement translates into the need for occupying a much wider spectrum and using more power to deliver high-rate information between a base station (BS) and user equipment (UE), such as a mobile terminal. However, portable devices, with their battery power and low build costs, generally are not well suited for transmitting wideband signals at high power. Further, while base stations are not considered power limited in the same sense as mobile terminals, excessive power consumption at base stations is nonetheless undesirable. And, beyond that, the variation in channel conditions throughout a given base station's service area generally means that one or more areas are hard for the base station to transmit into, at least at the high signal qualities needed for the higher data rates.
Relay stations, which are also referred to as repeaters, address at least some of these problems, and they represent an area of rapidly growing interest. In one contemplated approach, the insertion of repeaters into a base station cell provides improved coverage for high bit-rate services. The LTE and LTE Advanced standards involve high data rates, e.g., the LTE downlink may achieve 100 Mbps or higher, and the LTE Advanced downlink may achieve 1 Gbps or higher. Without repeaters, it may not be possible for a mobile terminal or other item of user equipment to transmit such signals to a supporting base station, and vice versa.
Known repeaters separate into various categories, based on core aspects of repeater structure and operation. For example, there are regenerative and non-regenerative repeaters. Broadly, a regenerative repeater receives a signal, reconstructs it, and transmits the reconstructed signal. Such reconstruction enables the signal to be repeated over multiple hops—over several repeaters, for example—without significant degeneration. Non-regenerative repeaters, on the other hand, simply repeat the received signal.
Other distinctions relate to reception and transmission frequencies. A frequency-translating repeater repeats the received signal, but does so at a different frequency. That is, the received signal is translated into a different frequency (or frequencies) for transmission. One advantage of this arrangement is the elimination (or significant reduction) of input-to-output leakage. Repeaters operating on the same receive/transmit frequency rely on input-to-output isolation to prevent undesired transmit/receive coupling, which can cause repeater instability.
However, while frequency translation provides for good input-to-output isolation, it complicates or prevents in-band channel signaling between a base station and its repeater-supported user equipment. As such, frequency translation generally is not compatible with the existing communication standards between base stations and user equipment, such as GSM/WCDMA/LTE, etc.
In general, however, known relay systems include multi-hop MIMO relays, for use in extending high-rate service in advanced wireless systems, such as LTE Advanced. In this context, both regenerative and non-regenerative relays are known. Further, to a limited extent, some types of frequency translation appear to be known, such as where a MIMO OFDM relay maps the information received on one OFDM subcarrier/symbol time, into another OFDM subcarrier/symbol time, where “OFDM” denotes Orthogonal Frequency Division Multiplexing.
See, for example, U.S. Pat. No. 7,184,703 B1, which discloses MIMO relay stations that appear to use signal SNR evaluations to determine which uplink/downlink signals will be relayed. In one or more embodiments, the relays use regenerative transmission, with the possibility of in-band frequency translations. Further, see U.S. Pat. No. 7,218,891 B2, which discloses relays that use in-band transmissions, with a focus on coordinated rate and power control, to allow simultaneous transmissions between a base station and user equipment, and between a relay and user equipment.
Still further, the reader may refer to U.S. Pat. No. 7,386,036 B2 for an example of link optimization between MIMO relay stations and users that is done separately from the optimization of relay-to-base-station links. And U.S. Pat. No. 7,406,060 B2 discloses MIMO relay stations, where communication channels between the relays allow them to operate with Space Time Transmit Diversity (STTD), or with Space Time Block Coding (STBC).
Finally, see Fizvi, Sun, et al., “Fractional Frequency Reuse for IEEE820.16j Relaying Mode,” submitted as Paper No. IEEE C80216j-06—223 to the IEEE 802.16 Multihop Relay Project (2006-11-07). This paper discloses a fractional frequency reuse (“FFR”) scheme, wherein a full load frequency reuse of one is maintained for (cell) center users, while FFR is used for (cell) edge users, to improve edge user connection quality. In other words, in this context, cell edge users operate with a fraction of the available sub-channels, based on a relay between the base station and the cell edge users relaying only a portion of the frequencies in use.